1. Field of the Invention
The present invention relates to an improved method for the synthesis of desferrioxamine B and analogs and homologs thereof.
2. Description of the Prior Art
The microbial iron chelator, siderophore, desferrioxamine B [N'-[5-[[4-[[5-acetylhydroxyamino)pentyl]amino-1,4-dioxobutyl]hydroxyamino ]pentyl]-N-(5-aminopentyl)-N-hydroxybutane diamide] was isolated from Streptomyces pilosus and characterized by Bickel ["Metabolic products of actinomycetes. Ferrioxamine B," Helv. Chim. Acta., Vol. 43, pp. 2129-2138] in 1960. It is a linear trihydroxamate ligand which forms a very stable hexacoordinate, octahedral [Modell et al, "The Clinical Approach to Thalassaemia," Grune and Stratton, London, p. 217-241 (1984)] complex with re (III), K.sub.f =1.times.10.sup.30 M.sup.-1. The ligand employs its three bidentate hydroxamate units in chelating metal ions.
Although desferrioxamine B will bind a number of different +3 cations, e.g., Al (III), Ga (III), Cr (III), it exhibits a high specificity for Fe (III), and is utilized by Streptomyces pilosus for the acquisition of iron from the environment. Because of the ligand's metal selectivity and low toxicity, it has been employed in the treatment of several iron overload diseases, e.g., thalassaemia ["Development of Iron Chelators for Clinical Use," Martell et al, eds., Elsevier, North Holland; New York (1981)]. However, desferrioxamine B does not offer a completely satisfactory solution to the iron overload problem. The drug is cleared by the kidneys and has a very short half-life in the body; thus, the patient must be maintained on constant infusion therapy. It is not orally effective. Because of these shortcomings, investigators have explored the potential of other ligands as therapeutic iron chelators. To date, these investigations have not included modification of the desferrioxamine molecule simply because of the lack of high yield of facile approaches to the synthesis of the molecule.
Desferrioxamine B was first synthesized in 1962 by Prelog et al ["Metabolic products of actinomycetes. Synthesis of Ferrioxamines B and D," Helv. Chim. Acta., Vol. 45, pp. 631-637 (1962)]. However, because of the number of steps in the synthesis and the low yield of the sequence, the method does not enable the production of large quantities of the chelator or its analogs. A retro-synthetic analysis of the ligand reveals that the desferrioxamine molecule is made up of two fundamental units: 1-amino-5-(N-hydroxyamino)pentane and succinic acid. The key to its synthesis is the production of this amino-hydroxyaminopentane unit and its condensation with succinic acid. Prolog approached this problem beginning with the starting material 1-amino-5-nitropentane, an amine which was accessible in only 46% yield [Bickel et al, "Metabolic products of actinomycetes. Isolation and synthesis of 1-amino-5-(hydroxyamino)pentane, an essential hydrolysis product of ferrioxamine and ferrimycin," Helv. Chim. Acta., Vol. 43, pp. 901-904 (1960)]. This compound was next N-carbobenzoxylated and the terminal nitro group reduced to the corresponding hydroxyamino group. This key intermediate was condensed with succinic acid followed by a series of other dicyclohexylcarbodiimide catalyzed acylations along with several reductions to produce desferrioxamine B. The overall yield of this eleven step sequence was 6%.
Bergeron et al ["An Efficient Total Synthesis of Desferrioxamine B," J. Org. Chem., Vol. 53, pp. 3131-3134 (1988)] reported a total synthesis of desferrioxamine B (DFO) in which the construction moved from the N-acetyl to the primary amine end of the molecule.
It is an object of the present invention to provide novel, improved, high yield methods for the production of desferrioxamine B and homologs and analogs thereof, which proceeds in the opposite direction from that of Bergeron et al, supra, and avoids some of the problems associated with the reduction steps involved therein, is of high overall yield and begins with easily accessible starting materials.